US3212721A - Grinding apparatus for treating fibrous material - Google Patents

Description

Oct. 19, 1965 A. J. A. ASPLUND ETAL GRINDING APPARATUS FOR TREATING FIBROUS MATERIAL Filed Sept. 20, 1962 2 Sheets-Sheet 1 as 265s 78 162 1b 18 92L8 65 221 21 34 12F 38 1.4 67 I 25 ze a 2 so '71 4 oo 1 7 101 152 99 96 100 INVENTOR.

ARNE JOHAN ARTHUR ASPLUND et a1 ERIC Y. MUNSON Oct; 19, 1965 A. J. A. ASPLUND ETAL 3,212,721

GRINDING APPARATUS FOR TREATING FIBROUS MATERIAL Filed Sept. 20, 1962 2 Sheets-Sheet 2 Fig. 3

o u. 67 g 31. 10 26 -3011s 120 18 eo-1?;@ -62 INVENTOR. ARNE JQHAN ARTHUR AS LUND,

et a1 B ERIC Y. HUNSON United States Patent 3,212,721 GRINDING APPARATUS FOR TREATING FIBROUS MATERIAL Arne Johan Arthur Asplund, Bromma, Rolf Bertil Reinhall and Lars Ientn, Lidingo, and Sven Herbert Johansson, Bromma, Sweden, assignors to Defibrator Aktiebolag, Stockholm, Sweden, a body of Sweden Filed Sept. 20, 1962, Ser. No. 224,958 Claims priority, application Sweden, Sept. 22, 1961, 9,461/ 61 8 Claims. (Cl. 24137) This invention relates to grinding apparatus for treatment of fibrous material.

More particularly this invention relates to grinding apparatus such as defibrators and refiners for treatment of fibrous material comprising a rotatable and a rotationally stationary grinding member, both of which have disc form, for example. The rotatable grinding member is supported by a shaft and axially displaceable by means of a fluid-actuated servomotor for adjusting the interspace between the grinding members and producing a grinding pressure therebetween.

In disc refiners the spacing or gap between the grinding discs is not constant but varies with the pressure exerted on said discs by the material to be ground when it passes therebetween. On an increase of the quantity of the material fed into the gap between the discs said gap must be adjusted anew if it is desired to maintain the grinding interspace unchanged. This is the consequence of elongations or stretches in those parts of the apparatus which are subjected to tensile forces, and of compressions in those parts which are subjected to pressure. In general apparatus of the kind in consideration are operated with so small grinding gaps that the elongations and compressions, respectively, occurring in the various parts of the apparatus are considerably larger, such as ten times larger, than the grinding gap. If the supply of pulp ceases for some reason the grinding discs may come into metallic contact with each other.

It has already been proposed to avoid this drawback by inserting into the supply conduit for the material to be ground or the pulp a pressure-responsive relay which when the pressure in the conduit decreases or ceases actuates the grinding discs so as to prevent them from abutting against one another. The relay can also affect the driving motor for the rotatable disc so as to put said motor out of operation when the pressure in the pulp supplying conduit falls below a predetermined value. This system can be employed only when the pulp is pumped between the grinding discs but not when the pulp is introduced between the grinding discs by means of a screw conveyor or in a disc refiner operating under steam pressure. A further disadvantage with the system in consideration is that the apparatus must be started manually or the spacing between the grinding discs be adjusted when the pressure on the pulp supply conduit decreases.

It has further been proposed to cause the pressure in the pulp supply conduit to govern the spacing between the grinding discs through intermediation of a hydraulic servomotor, for example. This pressure is, however, not in proportion with the stretches or compressions produced in the apparatus parts, for which reason it is not possible to keep the spacing between the grinding discsconstant in the proposed way.

One main object of the present invention is to provide an improvement of the grinding apparatus with regard to "Ice the drawbacks indicated hereinbefore. A further object of the invention is to bring about the desired improvement of the grinding apparatus by providing means adapted to cause a displacement of the rotatable grinding member relative the stationary grinding member in response to the pressure produced between the grinding members, and thereby to keep the gap between the grinding members at a predetermined value.

Further objects and advantages of the invention will become apparent from the following description considered in connection with the accompanying drawings, which form part of this specification and of which:

FIG. 1 is a vertical longitudinal section through a disc refiner constructed according to the invention. FIGS. 2 and 3 are similar sectional views of two alternative embodiments of the invention. In the various figures equivalent parts have been denoted with the same reference numerals.

Referring to the drawings,reference numeral 10 denotes a base of a grinding apparatus, ashaft 12 being supported in said base by twobearings 14 and 16, respectively. Thebearing 14 is located in an interior bearingcasing 18 and together with this latter member is axially displaceable within anouter bearing casing 20. In the same manner thebearing 16, which is a combined axial and radial thrust bearing, is axially displaceable together with an inner bearing casing 22 within an outer bearingcasing 24. Theshaft 12 carries a rotor 25, onto which agrinding disc 28 is rigidly secured and thus is rotated together with the shaft. Astationary grinding disc 30 is fastened by means of bolts to acasing 32, divided at a horizontal level above the shaft. The material to be ground is fed into the apparatus through acentral channel 34 formed in thecasing 32 and conveyed in an outward direction between thegrinding discs 28 and 30, where it is disintegrated. Disposed in the base part of thecasing 32 is a discharge opening 36 for removal of the ground fibrous material.

A hydraulic servomotor, generally denominated 38, is provided around theshaft 12. Said servomotor comprises acasing 40 which may be made integral with thebearing casing 24, and apiston 42, which is concentric with and, with play, surrounds theshaft 12 and bears against the inner casing 22. Thepiston 42 has acentral flange 44, axially movable within thecasing 40.

Rigidly secured to thecasing 40 of the servomotor is apilot valve 45. Said pilot valve comprises apiston 46 provided with a central flange 47 and twolateral flanges 48 and 50. It has acentral chamber 52 and twolateral chambers 54 and 56 adjacent of which the inner diameter of the valve suits to the outer diameter of the flanges. The axial dimension of thepiston 46 is kept below the longitudinal dimension of thechamber 52 by a very small value such as one hundredth or a few hundredths of a millimeter. In the same manner theflanges 48, 50 have an axial dimension which is only inconsiderably minor than the longitudinal dimension of thechambers 54 and 56. In a middle position all flanges are straight in front of their respective chambers.

Apipe 58 connecting thecentral chamber 52 of the pilot valve with anoil sump 60 is provided with apump 62 and connected with areturn pipe 63 controlled by a spring-loadedvalve 64. From aspace 65 of reduced diameter equal with that of the flanges, which is located between thechambers 52 and 54 of the pilot valve apipe 66 leads to thechamber 67 located on one side of theflange 44 of theservomotor 42. Apipe 68 connects a further space 69 of reduced diameter of the pilot valve located on the other side of thecentral chamber 52 with achamber 70 located on the opposite side of the flange 44-. Thelateral chambers 54, 56 are in connection with thesump 60 throughreturn pipes 71 and 72.

Anarm 74 rigidly secured onto thepiston 42 of the servomotor carries a set screw '76, screwed in thereto and extending coaxially with thepilot piston 46 and adapted to act on the end of said piston projecting out of the valve casing. The opposite end of said piston is loaded by aspring 78 tending to displace the piston towards the set screw.

Acylinder 80 secured to thearm 74 houses a piston movable therein and on both sides subjected to the action ofspring membranes 83, 84. The upper side of thecylinder 80 is through apipe 86 in connection with the space 69 of the pilot valve, the lower side of said cylinder being connected through apipe 88 with thespace 65. A pin 90 rigidly secured to thepiston 82 projects out of thecylinder 80 between thepiston 46 and theset screw 76 where said pin has the shape of a wedge or aguide cam 92.

The device operates in the following manner:

From thesump 60 thecentral chamber 52 of the pilot valve is fed with oil of constant pressure through thepipe 58. In FIG. 1 thepiston 46 is shown in a neutral middle position, in which the pressure oil is distributed equally to thespaces 65 and 69, the pressure thus being the same in these as well as in the bothchambers 67 and 70 of the servomotor. If thepiston 46 is moving to the left in the figure, the pressure will increase in the space 69, while it will decrease in thespace 65. This is due to the fact that the middle flange 47 opens a bigger connecting area between thecentral chamber 52 and the space 69 at the same time as thelateral flange 50 chokes the passage between the space 69 andpressureless chamber 56. On the other hand the connection between thespace 65 and themiddle chamber 52 is choked and further a bigger passage is opened between thespace 65 and the pressurelesslateral chamber 54. This results in that a higher pressure acts on thepiston flange 44 of the servomotor in thechamber 70 than in thechamber 67. If thevalve piston 46 moves in the opposite direction the result will be reversed, which means that the pressure increases in thechamber 67 and decreases in thechamber 70 of the servomotor. The material to be ground fed between the grindingdiscs 28 and 30 is thus subjected to a pressure the magnitude of which depends on the position of thepiston 46 of the pilot valve and which is determined by means of theset screw 76.

Thepiston 46 of the pilot valve is kept by thespring 78 continuously pressed against the adjustingscrew 76 and thus follows the latter in its axial movements. In case the pressure between the grindingdiscs 28 and 30 increases due to the accumulation of material in the gap between said discs and therotating grinding disc 28 together with thepiston 42 is displaced to the left, theset screw 76 is entrained also, since it is secured to thearm 74 connected with thepiston 42. Thepiston 46 of the pilot valve follows with theset screw 76. The result will be in accordance with the operative steps explained above that the oil pressure increases in the space 69 of the pilot valve and consequently in thechamber 70 of the servomotor also. In thechamber 67 of said servomotor the oil pressure will be reduced in a corresponding degree. An increased pressure is mobilized to act on thepiston 42 of the servomotor in order to restore the earlier gap between the grinding discs. This gap is desired to be of an order of magnitude of only one hundredth or some hundredths of a millimeter. If, on the contrary, the grinding discs, due to non-arrival of fed material, should tend to approach one another, thepiston 42 of the servomotor and theset screw 76 will follow and cause thepiston 46 of the pilot valve to move to the right hand. This movement will result in an increase of the pressure in thespace 65 of the pilot valve and in thechamber 67 sure.

of the servomotor and a corresponding reduction of the pressure in the space 69 and thechamber 70 of the servomotor. Due to the feature that the difference in the axial dimensions of theflanges 47, 48 and 50 of thepiston 46 of the pilot valve and the longitudinal dimensions of thechambers 52, 54 and 56, respectively, surrounding said flanges, is very small, as was set out hereinbefore, thepiston 46 needs to be displaced over extremely small distances only for creating a change of the grinding pres- By readjustment of theset screw 76 the magnitude of the gap between the grindingdiscs 28, 30 can be increased or decreased as desired. It is easily understood that the piston of the servomotor and the pilot valve opera ate under mutual actuation on one another to adjust the grinding pressure in response to the magnitude of the grinding gap.

The wedge-formedmember 92 and the members cooperating with said member have as their object to compensate for the compressions and stretches, respectively, which appear in the apparatus parts transmitting the grinding pressure. As during the grinding operation a pressure is exerted on the piston of the servomotor in a direction towards thestationary grinding disc 30, the apparatus parts participating in the pressure transmission will be compressed, while an elongation or stretching will take place in those parts of thebase 10, which are located between this grinding disc and thecasing 40 of the servomotor. This compression and elongation amount, as already stated, to many times the size of the grinding gap. The elongation causes the casing of thepilot valve 45 to be displaced to the left. The effect of the compression and the elongation is thus accumulated with regard to the change of position between theset screw 76 and thevalve casing 45. When the parts exposed to pressure are compressed, theset screw 76 is evidently moved to the right in FIG. 1. Without thecam member 92 thepiston 46 of the pilot valve due to this change of position would choke the connection between thepressure chamber 52 and the space 69 and in corresponding degree open the connection between the pressure chamber and thepressureless chamber 56, so as to cause a reduction of the pressure in thechamber 70 of the servomotor, whereas in thechamber 67 of the servomotor the result would be reversed.

It will be easily understood from these explanations that if the gap between the grinding discs tends to increase an increased pressure is produced in the space 69 of the pilot valve. This increased pressure is transmitted through thepipe 86 to thecylinder 80 so as to cause its'piston 82 to be displaced downwards. As a consequence thecam member 92 is also moved downwards and thereby admits a displacement of thepiston 46 of the pilot valve to the left. This displacement is dimensioned so as to correspond to the compression of the apparatus parts exposed to pressure and the elongation or stretching of the parts subjected to drawing stresses. In this way thepiston 46 can be kept in such a position in relation to the casing of the pilot valve that the pressure acting in the chamber '70 of the servomotor is the pressure required for the performance of the grinding operation with the desired and predetermined grinding gap. The axial position of thepiston 46 is thus governed not only by theset screw 76 but also by thecam member 92 and the total effect of their actions is to pay attention also to the compression and elongation in the apparatus.

FIG. 2 shows an embodiment with a mechanically operating device for compensation of the compression and the elongation in the apparatus. Rigidly secured to thecasing 32 is abracket 96 in which one end ofarod 98 is pivotable about a pivot 100. The other end of the rod is connected to apivot 101 on alink 102 which is mounted on thepivot 103 in abracket 104 rigidly secured onto the outer bearing casing 24 integral with thecasing 40 of the servomotor on one hand, and on apivot 106 of thecasing 45 of the pilot valve. Thebar 98 has a length approximately corresponding to the length of that part of the base of the apparatus which is subjected to elongation due to the action of the grinding pressure. Thepivot 101 of thebar 98 is located between thepivots 103 and 106 and causes thearm 102 due to the elongation to turn clockwise according to FIG. 2, relatively to thebracket 104. Thecasing 45 of the pilot valve is thus displaced to the right. The length of the levers represented by the spacing between thepivots 101 and 103 at the one hand and thepivots 103 and 106 is determined so as to take into consideration also the compression in those parts which transmit the grinding pressure from thepiston 42 of the servomotor to thecasing 32 and which in accordance with the explanation above cause a displacement of theset screw 76 in the right-hand direction in the figure. Thecasing 45 of the pilot valve will in other words take such a position in relation to thepiston 46 of the pilot valve adjacent theset screw 76 as if no compression nor elongation had taken place. Otherwise, the hydraulic system operates in the same manner as described hereinbefore in connection with FIG. 1.

In the embodiment according to FIG. 3 thepiston 42 of the servomotor cooperates with a stationary stop which in a manner known per se determines the minimum of the width of the grinding gap existing between the grindingdiscs 28 and 30. According to the figure said stop consists :of aring 110 screwed onto the part of the piston of the servomotor projecting out of thecasing 40. The piston of the servomotor cannot be moved more towards the rotationally stationary grinding disc than until the ring 100 bears against theend face 112 of themotor casing 40. Thering 110 is to determine the width of the grinding gap to assume a desired value.

In this embodiment there is no pilot valve. Instead thechambers 67 and 70 of the servomotor havepipes 112 and 114 respectively, opening thereinto and adapted to become connected by means of amulti-way valve 116 with tone or the other of twopipes 118, 120, respectively, of which the former opens to the pressure side of thepump 62 and the latter into thesump 60. In the position ofvalve 116 shown in the FIG. 3 thepressure pipe 118 is in connection with thepipe 114. Thechamber 70 of the servomotor is thus under pressure, while thechamber 67 is over thevalve 116 connected to thereturn pipe 120 and without pressure. By turning the valve by 90 the pressure fluid is instead fed into thechamber 68, whereas thechamber 70 becomes pressureless.

Thering 110 is on its external face provided with teeth engaging agear 122, carried on ashaft 124 of an electric motor 126. Provided on thecasing 32 is anelongation meter 128 at a place subjected to elongation due to the action of the grinding pressure produced between the grind-ing discs. Thi meter is in a manner known per se of such type as to have its electrical resistance to vary with its length. The elongation meter is connected to a :relay 130 which amplifies the impulses emitted the meter and transmits them to the electric motor 126 through awire 132. The elongation meter thus sends impulses to the electric motor 126 in response to the changes in elongation corresponding to variations of the grinding pressure. If the gap between the grinding discs is increased due to an increased supply of material to be ground and as a consequence the elongation and compression in the apparatus parts are increased also, theelongation meter 128 causes the electric motor 126 to operate and to turn thering 110 so as to become unscrewed, i.e. towards the left in the figure.

Therotating grinding disc 28 is thus capable of main taining that position relative thestationary grinding disc 30 which corresponds to the width of the determined minimum gap. On a reduction of the elongation, as a consequence of a reduction of the grinding pressure the motor screws thering 110 in the direction towards the casing 40 of the servomotor so as even now to produce a compensation and under all circumstances to prevent metallic contact between the grinding discs.

While several more or less specific embodiments of the invention have been shown and described, it is to be understood that this is for purpose of illustration only, and that the invention is not to be limited thereby, but its scope is to be determined by the appendant claims.

What we claim is:

1. In a grinding apparatus for treatment of fibrous material comprising a rotatable and non-rotative grinding member, of which the former includes a shaft supporting said rotatable grinding member and axially displaceable by means of a servomotor piston adapted to be actuated from both sides by a fluid for adjusting the spacing between said grinding members and for producing a grinding pressure between the same, means to actuate the piston of the servomotor, said means being adapted to cause a displacement of the rotatable grinding member relative the grinding member in response to compression and elongation, respectively, produced depending on the grinding pressure, in the pressure transmitting parts of the apparatus so as to keep the gap between the grinding members at a predetermined value.

2. In a grinding apparatus as claimed in claim 1, a part of electric elongation meter disposed on an apparatus exposed to elongation, a motor actuated by said elongation meter and a driving mechanism connected with said motor and adapted on actuation by an impulse from said elogation meter to displace the piston of the servomotor relatively to the casing surrounding said piston in response to the elongation or compression produced in the apparatus.

3. In a grinding apparatus as claimed in claim 1, conduits on each of both sides of said servomotor piston in connection through a pilot valve with a pressure source and with an outlet, respectively, the pilot valve having a stationary cylinder and a movable piston which are displaceable in relation to one another for adjustment of the grinding pressure exercised by said servomotor piston in response to the relative position between said piston and a base part of the apparatus exposed to elongation, the apparatus further comprising an element adapted to counteract a change in the relative position of the parts of said pilot valve caused by the compression and elongation produced in said base.

4. In a grinding apparatus as claimed in claim 2, adjusting means adapted to determine the position of the movable piston of the pilot valve, said adjusting means being connected with the piston of the servomotor and adjustable for alteration of the mutual position of said movable pilot valve piston and said servo-motor piston.

5. In a grinding apparatus as claimed in claim 3, said element being disposed to be under actuation by a pressure diiference of the fluid created in the pilot valve for causing a displacement of the movable piston of said pilot valve relative to the servomotor piston so as to correspond to the displacement caused by the compression and elongation of the piston relative to the surrounding casing of the servomotor but in a direction opposite to said displacement.

6. In a grinding apparatus as claimed in claim 2, the pilot valve having its piston movable in relation to its cylinder but stationary in relation to the piston of the servomotor, said cylinder being stationary in relation to a place located on the base of the apparatus adjacent the stationary grinding member.

7. In a grinding apparatus as claimed in claim 4, said element having the form of a cam-like member determining the position of the piston of the pilot valve relative to said adjusting means and being displaceable by means of a piston-like member located in a casing in response to the pressure exercised by the fluid on the piston of the servomotor, said cam-like member having a surface formed so as to cause the spacing between said adjusting means and the piston part of said pilot valve to be corrected in correspondence to the compression and elongation produced in the base of the apparatus.

8. In a grinding apparatus as claimed in claim 6, said cylinder of the pilot valve being connected with said place located on the base of the apparatus through a bar and a gear so as to cause the relative displacement of said cylinder relative to the piston part of the pilot valve to increase more than the valve corresponding to the elongation and thus also includes a change of position of the piston of the servomo-tor due, to the compression of the apparatus parts exposed to pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,548,599 4/51 Garr 241-37 2,971,704 2/61 Johansson 241-37 FOREIGN PATENTS 111,803 11/40 Australia.

J. SPENCER OVERHOLSER, Primary Examiner.

Claims (1)

1. IN A GRINDING APPARATUS FOR TREATMENT OF FIBROUS MATERIAL COMPRISIUNG A ROTATABLE AND NON-ROTATIVE GRINDING MEMBER, OF WHICH THE FORMER INCLUDES A SHAFT SUPPORTING SAID ROTATABLE GRINDING MEMBER AND AXIALLY DISPLACEABLE BY MEANS OF A SERVOMOTOR PISTON ADAPTED TO BE ACTUATED FROM BOTH SIDES BY A FLUID FOR ADJUSTING THE SPACING BETWEEN SAID GRINDING MEMBERS AND FOR PRODUCING A GRINDING PRESSURE BETWEEN THE SAME, MEANS TO ACTUATE THE PISTON OF THE SERVOMOTOR, SAID MEANS BEING ADAPTED TO CAUSE A DISPLACEMENT OF THE ROTATABLE GRINDING MEMBER RELATIVE THE GRINDING MEMBER IN RESPONSE TO COMPRESSION AND ELONGATION, RESPECTIVELY, PRODUCED DEPENDING ON THE GRINDING PRESSURE, IN THE PRESSURE TRANSMITTING PARTS OF THE APPARATUS SO AS TO KEEP THE GAP BETWEEN THE GRINDING MEMBERS AT A PREDETERMINED VALVE.

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